Method and means for focusing sound caused by aircraft



May 31, 1960 l.. E. FoGARTY 2,938,682

METHOD AND MEANS EDR EocusNG souND CAUSED BY AIRCRAFT Filed Sept. 17, 1954 2 Sheets-Sheet 1 A@ A w ATTCRN EY May 3l, 1960 L, E. FoGAR-rY METHOD AND MEANS FOR FOCUSING SOUND CAUSED BY AIRCRAFT 2 Sheets-Sheet 2 Filed Sept. 17, 1954 INVENTOR V.. T Dn A G O F E E C N E Dn U A f l l BY ATTORNEY 2,938,682 METHOD AND MEANS Fon FocUsnvG SOUND CAUSED BY AIRCRAFT Laurence E. Fogarty, Binghamton, N.Y., assigner to General Precision, Inc., a corporation of Delaware Filed Sept. 17, 1954, Ser. No. 456,786

8 Claims. (Cl. 244-77) My invention relates to a method and means for projecting energy disturbances caused by passage of an Yair'- borne object at supersonic speed through a uid medium to a predetermined point, and in particular to method and means for creating intense disturbances at a target point for offensive purposes. When an object passes through a fluid medium at a speed which is equal to or greater than the critical speed, or speed of wave propagation in the medium, such object creates a pressure disturbance vmanifested in shock waves. Early test igfhts of `aircraft capable of ight at sonic or supersonic speeds during dives caused considerable disturbance and some property damage until sonic dives near populated areas were prohibited. My invention describes method and means for greatly intensifying or concentrating such disturbances ata predetermined target point or area, so that no major damage to property and morale may be accomplished.

' It is therefore a primary object of my invention to provide a method for concentrating or intensifying to a remote point energy disturbances caused by passage of an object through a uid medium.

It is another object of my invention to provide a methodand means for concentrating or intensifying sound created by passage of Van aircraft at sonic or supersonic velocity through the air to a remote target point.

It is a further object of the invention to provide means by which the pilot of an aircraft may determine the correct ight path Vat sonic lor supersonic speeds in order to `concentrate or intensify energy disturbances to a remote point or area. y It is yet another'object of the invention to provide means by which a pilotless missile may be automatically guided so as to concentrate or intensify energy disturbances caused by sonic or supersonic flight to a remote target point.

Other objects of the invention will in and will in part appear hereinafter.

-The inventionaccordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

` For a fuller understanding of the nature and objects of the linvention reference should be hadto the following detailed description takenV in connection with the accompanying drawings,'in which:

Fig. 1 is a velocity diagram of an aircraft traveling at supersom'cl speed in relation to a target point;

Fig. 2 is a schematic diagram of an assembly by means of which the pilot of an aircraft may sight a target point part be obvious Order to focus or concentrate sound wav'es to the'targetv sight;

Fig. 4 is a geometric diagram useful in understanding the operation of the apparatus of Fig. 3;

Fig. 5 is a plan 'View of a typical flight path;

Fig. 6 is a schematic diagram of a guidance system by means of which a pilotless missile may be caused to ily -the correct Hight-path so as to concentrate sound waves generated by sonic or supersonic iiight to a remote point'. In Figs. 2, 3 and 5 certain conventional parts are shown in block diagram form for sake of clarity.

Assume that an aircraft is travelling at sonic or supersonic speed in a stationary isothermal atmosphere. Travel at supersonic speed in a straight line generates a coneshaped envelope of waves which is denominated the shock front. Assuming that the dimensions of the aircraft-are small vcompared with the distances travelled, a

shock wave may be considered to be a soundwave of great intensity which decreases in intensity as its distance from the source increases, so that the sound waves generated may be considered as emanating from a moving point. At each instant, the waves generated by the moving point will decay to sound waves of decreasing intensity as they travel'in all directions from the point at the speed of sound. I have discovered ,that if the sound waves generated duringa nite length of time are caused to -arrive simultaneously at a target point, a very intense disturbance will be created at the target point. To make such waves arrive simultaneously at the target point it has been found necessary that the aircraft move toward -the target point at the speed of sound. If the speed of theaircraftis greater than the speed of sound,'it is'necessary that the component of aircraft speed in the direc- V cos 0=a Since z2-jg where 'M` equals Mach Number,

flef

V cos 0;

cos 0= `0--arc cosl M e Hence it may be seen that the angle between the aircraft ightpath and target must bernaintained at 1 arc cos M and that as long as such an angle is maintained, sound waves generated throughout a finite length of time will converge onthe target point at a particular instant.

Referring to, Fig. 2 there is shown schematically an apparatus jby,which the pilot of a high speed aircraft may be enabled to ily the proper ight path so as to concentrate the sound waves generatedto a target point. `Located directly forward of the pilots station and accessible tothe eye 10 of the pilot is a telescope 12 having conventionallenses. Telescope 12 is pivotally mounted scope 12 and pinion 15 meshes with gear sector y14 to- Y 3 n rotate telescope .12 through -the angle a. The shaft end portion 16 of yoke 13 is mounted along the longitudinal axis of the aircraft in bearing 17. Handle 18 is rigidly attached to telescope 12 toeallow manual rotation of the assembly around shaft 16. At sonic land supersonic speeds the angle of attack of most aircraft is very small (less than onedegree), and hence rthe longitudinal axis of the aircraft may be considered to correspond tov the aircraft flight path. In alternative embodiments rof the' invention, the pivot point of telescope 12 may be located on the actual llight path by positioning shaft'16 relative to the aircraft longitudinal axis intaccordance with instantaneous angle of attack. For, example, shaft 16 may bel servo-slaved to a vane onthe nose of the aircraft. Pinion .15 is rotated by the output of a Y translator 19. Translator 19 may .take a variety of forms,- all of which serve to translate the inputquantity Mach number M to i rotary position. For example, translator 19 may consist of an arc-cosine cam and follower adapted to position a linear servomechanism. As another example, translator 19 may consist of a conventional electric servornechanism having an arc-cosine follow-up potentiometer wound nonlinearly to provide cos1-1 .y Y

M modification of the'Mach number input quantity. f Many modern high speed aircraft carry machmeters, andthe invention contemplates derivation of the input signal for translator 19 from the same apparatus presentlyV utilizedV Such a curve approaches` and reaches the target point in finite time if the target -has finite area. The invention contemplates the concentrating of sound waves during only a portion of ight along such a curve, since the rate of turn required near the target becomes prohibitive, and since it is necessary that the aircraft not follow such a flight path to such an extent that crashing into the ground or target might occur. As the pilot selects a target point, he maneuvers the aircraft so that the target point may be seen through telescope 12. Then he merely must fly the aircraftY so as to maintain the target within Ysight through the telescope. As long ras ight `is maintained at sonic or supersonic speed and the target point'is visible through telescope 12, sound waves will be concentrated at the target. When the lpilotreaches some critical point near the target, it will be necessary that -he'discontinue flying the particular ight Ypath directed bythe telescope.

Since sound waves emanate'in all directions from 1the and by mex/ement ef 'nasale iataeseope 12 is maneuveryable so that the sound generated in any one direction at a time may be concentrated on the target point. As movement of handle `18 rotates telescope 12 about shaft 16, all of the pointstoward which sound is being focused may be observed through the telescope, and hence the pilot may properly focus or concentrate the disturbances on a target point by maintaining the target Within sight through the telescope by combined movement of handle 18 and maneuvering of the aircraft. l

Referring to Fig. 3 there isV shown an alternative embodiment of the .invention which generally corresponds to the apparatus ofA Fig. 2 but in which the entire field i of view obtainable by rotation of the'tele'scope about the 15 aircraft longitudinal or flight path is presented at one time to the pilot to eliminate the need lfor manual rotation of the telescope. As the eye 10 of the pilot looks through'lenses 21 and 22, beam-splitter 23 and lens 24 toward the target, arring of light defining the allowable flight paths vis superimposed upon the area viewed through the telescope lenses. Light from a light source 25 which may comprise an ordinary lamp, is directed through a variable diameter reticule 26 and a projection'lens 27 to beam splitter 23. The variable reticule is of the type commonly used in stadiometric aerial gunsights, and serves to project a ring 'of light upon beam splitter 23. Ring gear 28 of the variable reticule is driven by pinion 29 tolvary the diameter of the light ring superimposed upon the scene viewed through the'telescope lenses. Pin` ion 29 is driven by translator 20 to provide a lightrfring having a diameter varying in Vaccordance with VMT-fl) As may be s'een in Fig. 4, if the desired ight path is to be defined by the diameter of a light ring, the diameter must be maintained in accordance with 2k tan 0, where k is a constant representing the optical distance ofthe light ring from the viewpoint. Since 0 has been shown to equal i cori-1M it will become apparent that 2k tan 0 will equal 2k\/M2=- l. Translator 20 may comprise any conventional non-linear translator which will provide the required function, such as a servo-mechanism employing a non-linear follow-up potentiometer, or a cam-follower arrangement suitable to modify the Mach number input quantity. Thus the` out-`v put from 'the translator 20 will serve to determine the size of the light ring superimposed on the scene vviexyvedV through lens 24,and by maneuvering the aircraft so that the target point is maintainedon thelight ring, the pilot will be enabled to y the correct pathft'oconcentrate sound 'disturbances'at the target. While I have illustrated translators 19 and 20 in Figs. l and 3, as providing speciiic output functions, it will berrealized that *non-linear that means be Vprovided for practicing the invention in such aircraft. Shown in Fig. 5 is a plan view o f aliight path carried out at a constant altitudejto focus or `conaircraft, itis not necessary at all that therspiralflight pathV be coniine'djtov aisingle plane. vThe', aircraft'travelling at sonicorsupersonic speed. 'generates' a fconefjof lsonic centrate sound on a targetfpoint T, which need not Dbe at the vsame altitude. It will be seen that theaircraft ap proaches fthe target point T in a logarithmic spiral. In order to concentrate soundon target point T, the angle 0,which`is the anglekbetween the target and a tangent to the flight path, must be maintained throughout the sound focusing period. Shownin Fig. 6 is a portion-of the apparatus which may be used to guide the pilotle'ssfair'-V craft along the'proper ight' path. A homing or track-V ing device, whichnmay comprise any yof the conventional radio orradar homing devices used inaerialgu'nneryland asassa t lnavigation, homes antenna 30 upon the target and providesan output quantity such as an analogue potential commensurate in magnitude and direction with the angle between the aircraft longitudinal axis or ight path and the bearing to the target. The quantity is applied to the turning circuit of a conventional aircraft automatic steering system through resistance R-L The output quantity'from translator 19 is proportional to the desired angle 0 between aircraft ight path and the target, and if'the signal `is appliedin opposite sense through resistance R-2, it will be seen that the automatic pilot will steer the aircraft so that both input signals are equal, at which time the aircraft will be ying the desired ight path. The autopilot may include conventional additional means (not shown) to maintain the aircraft at a constant desired altitude during 4the course of the attack.

During flight prior to a sonic attack, the guided aircraft may be steered by control inputs to the automatic pilot applied through terminal 99 and normally-closed contact a of relay K-17. Such control inputs may be derived in the usual fashion such as from radio signals, punched cards, etc. When radar antenna 30 has horned on a target, output Voltage may be derived from the radar range circuit inversely commensurate with range from the aircraft to the target. At a predetermined minimum range, the output voltage increases suflciently to actuate relay K-17, which disconnects the previously applied control quantities and applies the sonic focusing flight path signals through contact b of relay K17. The aircraft will then automatically ily the correct flight path so as to focus the sound on the target point. It will be seen that as the aircraft nears the target, the rate of turn required to maintain the ight path increases' exponentially to a very high amount. At a predetermined maximum rate of turn, a conventional aircraft accelerometer or rate gyro actuates switch S-l, de-energizing relay K17. Deenergization of relay K-17 re-connects the automatic steering system to its previous radio or pattern-controlled input and thereby causes the aircraft to resume normal flight. Switch S-1 may be suitably damped to close slowly, so that the aircraft may fly an appreciable distance away from the target before another sonic attack is begun. A conventional aircraft accelerometer is preferably used with apparatus utilizing an automatic steering system which makes co-ordinated turns, and since acceleration normal to the flight path will increase as the aircraft spirals to near the target point, a conventional accelerometer may be arranged to open switch S1 at a predetermined acceleration, such as the limit load factor of the aircraft. It will be apparent that photo-electric homing means may be used for night operations near populated areas instead of the radio echo-ranging means mentioned above.

While I have shown a guidance system which carries out a sonic attack at constant altitude, it will be apparent that such attacks may be made in other than horizontal planes, and furthermore, that an attack need not be confined to a single plane. Modificationof my guidance system to allow attacks in other planes and in non-planar spirals will become obvious to those skilled in the art in light of this disclosure. In constructing apparatus to provide focusing of sounds generated during travel at a varying altitude, it may be considered desirable to schedule the speed of sound` with altitude. For example, the function of the translators may be altered by a correction factor entered manually by the pilot, or automatically by air temperature or barometric pressure sensing means in accordance with conventional analogue computer techniques.

While I have described my invention as relating to energy disturbances created by the supersonic passage of one object through the fluid medium, it will be apparent that groups of physically separate objects may be guidedtogether along the required path to cause even greater disturbances at target points without def parting from the invention. v v

It will thus be seen that the objects set forth above, among-those made apparent from the 'preceding description, are efficiently attainedf Since certain changesk may be made in carrying out the above method and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted Ias illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specic features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

I. A method of concentrating energy disturbances caused by passage of an object through a fluid medium, comprising the steps of, moving an object above the critical speed of wave propagation in the general direction of `a remote point, guiding said object in a spiral path so as to maintain the component of velocity toward said point of said object equal to said critical speed, and diverting said object from said spiral path as said object nears said remote point.

2. A method of concentrating sound waves generated by passage of an airborne object at supersonic speeds through the aerodynamic fluid comprising the steps of moving an aircraft at supersonic speed, guiding said aircraft in a spiral path so that the component of velocity of said aircraft toward a remote point equals the speed of sound in the aerodynamic fluid, and diverting said aircraft from said spiral path as said aircraft nears said remote point. Y

3. An automatic guidance system for focusing shock waves generated over a finite length of time by sonic or supersonic ilight of an aircraft so as to cause said waves to arrive substantially simultaneously at a remote target comprising in combination first means for deriving a rst control quantitycommensurate with speed of ight, second means for deriving a second control quantity cornmensurate with direction of travel of said aircraft with respect to said target, means responsive to said control quantities for providing a steering control quantity commensurate with a desired direction of travel which will make the component of velocity of said aircraft toward said target substantially equal to the speed of sound, and steering means responsive to said steering control quantity for steering said aircraft.

4. Apparatus according to claim 3 in which said first means comprises means for deriving an analog computer quantity commensurate with Mach number of flight.

5. Apparatus according to claim 3 in which said second means comprises radio homing means.

6. Apparatus according to claim 3 in which said first means comprises means for deriving an analog computer quantity commensurate with Mach number of flight, said second means comprises radio homing means, means responsive to distance of said aircraft from said target for connecting said control quantities to said steering means, and means responsive to rate of turn of said aircraft for disconnecting said steering means from said control quantities.

7. A guidance system for automatically concentrating sound waves generated by supersonic flight of an aircraft at a remote target point, comprising, means for deriving a irst control quantity commensurate with Mach number of ight, means for deriving a second control quantity commensurate with relative heading of said aircraft from said remote point, computing means responsive to said iirst control quantity for deriving a rst steering control quantity commensurate with the 8 Y determined distance from said point and further means gperbleljinresponse to an acceleration of saidaircraft to disable said Steering means Vat a lesser distancefrorn said point' or ci v c References cited in the meer this patent UNITEDYSTATES PATENTS 2,416,468 van Auken eral. Nov. '5, 1946 2,576,135 Moseley V. r. Nov. 27, 1951 Schuck et al. Nov.V 13.1956 

